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Investigating pillar failure mechanism and pillar-support interaction using large-scale laboratory tests and bonded block models
Chaurasia, Akash
Chaurasia, Akash
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2024
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Abstract
Underground mining methods such as room & pillar and sublevel open stoping use pillars to provide natural stability to mine openings, ensuring the safety of workers and machinery. While extensive research has focused on pillar failure mechanics and safe design layouts, there are few studies that examine pillar-support interactions under controlled loading conditions to aid in the design of pillar support systems. To address this gap, this study utilized laboratory tests and a discrete element modeling approach known as the bonded block model (BBM) on limestone and coal to investigate pillar damage mechanisms and pillar-support interactions.
Small-scale laboratory compression tests (0.15 m x 0.15 m cross section) were performed on porous Texas Cream Limestone without support and large-scale laboratory compression tests were conducted on porous Texas Cream Limestone (0.5 m x 0.5 m cross section) and coal blocks (0.55 m x 0.55 m cross section), both with and without ground support, to evaluate strength, failure processes, and influence of support on pillar strength and deformation behavior at different W/H ratios. The large-scale tests allowed for the use of controlled conditions and the incorporation of full-scale support elements. The resulting laboratory data set was used to calibrate BBMs in both 2D using UDEC and 3D using 3DEC and evaluate their capability to simulate pillar deformation as well as ground support behavior. A tri-linear bond-slip model was found to be necessary to capture the non-linear behavior of the rockbolt load mobilization observed during the laboratory tests. Additionally, wire mesh and face plates were explicitly represented in 3DEC using built-in structural elements. After calibrating the BBMs, various support configurations not considered in the laboratory were simulated to predict pillar-support interaction in such cases.
Both large-scale laboratory tests and numerical simulations showed that while the peak strength remained unchanged with the installation of support, the post-peak behavior became more ductile, and the residual strength increased for all W/H ratios. Although rockbolts enhanced ductility and residual strength, when used in isolation, they were ineffective at retaining fractured material at the pillar side walls once spalling began. However, installing wire mesh prevented spalling and degradation of the specimen sides by maintaining a buffer zone of fractured rock, which inhibited dilatancy and total volumetric deformation, thereby mitigating hazards associated with pillar degradation and ground falls. Overall, these results suggest that the installation of ground support will not enhance the global stability of pillars under normal circumstances, but that can be effective in mitigating localized instability issues such as slabbing and spalling of rock material around the pillar periphery. The results of this study can serve as a basis for future modeling studies focused on evaluating the effects of support systems on pillar deformation behavior in various rock types and under different loading conditions, thereby optimizing support design for underground pillars.
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